I don't use any Modem. The only thing i am connecting with to my ISP right now is the D-Link Dir-645.
Turn OFF DNS Relay is only for the ISP DNS, but i donÄt have any Problem with that.
I am using No-IP as a DNS Service to use my PC from verywhere.
The predefined DynDNS are not changeable, so he has no idea that he has to go to No-Ip.com
Without the DNs usage the D-Link is useless for me, so i will send it back and boy a FritzBox.
Anyway, thanks for your fast help and respond.
Best Regards Therdp